Cleavable cross-linking reagents will be used to identify platelet surface receptors for thrombin, von Willebrand's factor and fibrinogen and to carry out nearest neighbor analysis of mobile membrane components during activation. Platelet adherence to subendothelium will be measured in the presence of purified glycocalicin, its fragments and antibodies to them. The initial relationships of surface glycocalicin and membrane-associated tubulin will be studied by immunoperoxidase, ferritin and colloidal gold labeling.